1. Field of the Invention
The present invention relates to a fuel supply system for automotive engines that can achieve enhancements in fuel economy and harmful exhaust gas purification.
2. Description of the Related Art
Engines for automobiles can be classified into a gasoline engine using gasoline, a diesel engine using diesel oil, and so on. The fuel supply system for supplying fuel to such automotive engines is shown, for example, in FIG. 1.
In FIG. 1, reference numeral 30 denotes a four-cylinder engine. The combustion chambers of four cylinders (not shown) of the engine 30 have four branch pipes of an intake manifold (not shown) connected thereto, respectively.
To this intake manifold (intake side) an air filter 10 is connected through an air flow sensor 20, an air hose 40, and a throttle valve 60. This throttle value 60 is opened or closed by an accelerator pedal 50.
Also, in the branch pipes of the intake manifold or the combustion chambers of the cylinders of the engine 30, injection nozzles 31 are provided so that fuel can be injected into the branch pipes or combustion chambers. Moreover, an output signal from the air flow sensor 20 is input to a microcomputer 70. Based on the output signal from the air flow sensor 20, the microcomputer 70 increase or decrease a quantity of fuel which is injected from the injection nozzles 31 in correspondence to an increase or decrease in the quantity of air which is drawn in.
Therefore, in a fuel supply system such as this, if the engine 30 is operated, then negative intake pressure will be produced within the intake manifold (not shown) through the combustion chambers. With this negative intake pressure, the air in the atmosphere is drawn into the air hose 40 through the air filter 10. When this occurs, the dust and the like contained in the air are collected with the air filter 10, and the air being passed through the air filter 10 is purified. This purified air is drawn into the combustion chambers of the cylinders of the engine 30 through the air flow sensor 20, air hose 40, throttle valve 60, and the intake manifold (not shown). On the other hand, fuel is injected from the injection nozzles 31 into the four branch pipes of the intake manifold (not shown) or the combustion chambers. This fuel is mixed with the air which is supplied to the engine 30. And after this fuel-air mixture has burned within the combustion chambers, it is exhausted into the atmosphere.
Also, if the throttle opening angle of the throttle valve 60 is increased or decreased by the operation of stepping on the accelerator pedal 50, the quantity of air which is drawn in through the air filter 10 will be increased or decreased and therefore the quantity of fuel-air mixture which is produced at the throttle valve 60 will be increased or decreased. At the same time, the quantity of fuel which is injected from the injection nozzles 31 to the four branch pipes of the intake manifold (not shown) is increased or decreased, so that the output of the engine 30 is increased or decreased.
To increase the output of the engine suddenly in the above-mentioned fuel supply system, the driver can step on the accelerator pedal 50 considerably to increase the throttle opening angle of the throttle valve 60.
However, in the early stage of this operation of stepping on the accelerator pedal 50, a phenomenon in which the gases in the engine 30 flow backward occurs. In this case, although the air intake quantity is reduced, the quantity of fuel injected from the fuel injection nozzle 31 is increased, so that the rich fuel-air mixture is drawn into the combustion chambers of the engine 30 and is not completely burned. As a consequence, in the early stage of the operation of stepping on the accelerator pedal 50 deeply, exhaust gases, such as carbon monoxide and hydrocarbon, harmful to the atmospheric environment or human body are exhausted form the engine 30 into the atmosphere and result in the primary causes of environmental pollution. Furthermore, there is a problem in that the engine output efficiency falls and therefore the operational performance of the automobile is reduced.
An air oversupplying device, such as a turbocharger or a supercharger, has been proposed as a means for resolving this problem. In the turbocharger, an air compressor is driven with a turbine revolved by exhaust gases so as to supply an above-normal quantity of air to an engine. In the supercharger, an above-normal quantity of air is supplied to an engine by the use of an air compressor coupled to an output shaft of the engine.
However, since this type of air oversupplying means is not constructed to be afterward provided in an engine completed as a single product, it is difficult to easily equip a conventional automobile with the air oversupplying means.
Further, since the air oversupplying means is operated using the exhaust gas discharged from an engine and the drive force generated by the engine, the engine is always under a load. As a result, it is necessary to set the revolution speed of the engine at a somewhat high value, in order to prevent the engine from stopping during idling. However, in the case where an automobile stops frequently at intersections or in traffic jams, an excessive quantity of fuel corresponding to the increased revolution speed of the engine during idling is consumed. This is undesirable in fuel economy.
Further, as mentioned above, since the air oversupplying means is operated using the exhaust has discharged from the engine or the driving force generated thereby, the quantity of air to be supplied to the engine cannot necessarily be precisely controlled according to the revolution speed of the engine.